There is unrelenting market demand for circuits that are smaller ze, use less power, are faster, and are easily scalable when compared to conventional devices. Few circuit elements, including analog to digital converters (ADCs), are left untouched by these ever-present market requirements.
An ADC is a circuit that samples an input analog signal (either voltage or current) and produces a digital signal (e.g., a binary signal) representing an amplitude of the input analog signal. One type of ADC is a successive approximation register (SAR) ADC.
Conventional SAR ADC technology has existed for some time. Generally, conventional SAR ADCs generate a digital code representing a magnitude of an input voltage. To produce the digital code, conventional SAR ADCs operate in two phases—a sampling phase and a bit trial phase. During the sampling phase, the input voltage is acquired in a circuit called a “sample-and-hold” that precedes the ADC. During the bit trial phase, the input voltage is compared against digitally-controlled test voltages to determine whether the input voltage is greater than, or less than, a particular test voltage. Typical SAR ADCs operate bit by bit, comparing the input voltage initially to a first test voltage that is an analog voltage value corresponding to a most significant bit (MSB) of the digital code, deciding a value of the MSB, and thereafter comparing the input voltage to a subsequent test voltage that is an analog voltage value representing a combination of the selected MSB value and a. candidate value for the next lower bit position. In conventional SAR ADCs, this process uses either a complicated state machine control circuit or a shift-register based control circuit and a register of flip-flops known as a Successive Approximation Register or SAR, The shift register indicates which bit is selected during the bit trial phase and the SAR register stores the results of the bit trial phase. The bit trial process operates incrementally across all bit positions from the MSB to a least significant bit (LSB) position of the digital code, at which time the digital code corresponds to the input voltage. The digital code is then output from the SAR. ADC. While conventional SAR ADCs are functional, as mentioned above, there is market pressure to shrink and simplify SAR ADC circuitry, reduce SAR. ADC power consumption, speed SAR ADC conversion time, and make SAR ADC circuitry scalable.
Accordingly, there are long-felt industry needs for methods and apparatus that improve upon conventional methods and apparatus, including methods and apparatus for a SAR ADC that is improved over conventional methods and apparatus.